This proposed research addresses fundamental issues of excitatory and inhibitory amino acid neurotransmission in the vertebrate central nervous system. Single-channel patch-clamp techniques will be used on identified classes of isolated neurons from the spinal cord of the lamprey, a well- established model for the neuronal basis of locomotor activity in vertebrates. The research will address l) whether lamprey neurons have a single class of receptors for both of the inhibitory amino acid neurotransmitters, glycine and GABA, 2) whether NMDA-induced membrane potential oscillations can occur in isolated neurons and, if so, the nature of the ion channels that underlie these oscillations, and 3) how amino acid responses and presynaptic calcium channels are modified by neuromodulators. This work is innovative in its application of single- channel patch-clamp techniques to a vertebrate neuronal network of known function. The collaboration matches the many years of experience in synaptic physiology of investigators at the Sechenov Institute's Laboratory of Evolution of Neuronal Interaction in St. Petersburg, Russia with the laboratory at Marquette University, Milwaukee, Wisconsin, which has extensive experience in characterizing identified cell types in the lamprey spinal cord. The proposed collaborative project would be part of an on-going study of how the vertebrate nervous system generates and controls locomotor activity. The parent grant R29 NS-28369, "The Role of Spinal Interneurons in Locomotion", will be enhanced and extended in this project by addressing neurotransmission using the much more sensitive and quantitative technique of single-channel patch-clamping of isolated neurons. Patch-clamp recordings will be made on morphologically-identified and/or tracer-labelled neurons, thus allowing comparisons with conventional intracellular recordings previously made within the intact spinal cord. Test solutions will be applied by a rapid concentration- clamp method, and ionic currents will be recorded either from detached membrane patches or as whole-cell currents. These studies will contribute to our basic understanding of synaptic function in the spinal cord, which ultimately will be important in the development of therapeutic measures to treat spinal cord injury and disease.